The invention relates to a method and apparatus for milking mammals, including cows.
Milking systems withdraw milk from the milk secreting glands of mammals by applying negative pressure, i.e. vacuum, to the teat. A plurality of teat cups are provided, each having a liner, or inflation, around a respective teat, and defining a milk flow passage within the liner below the teat, and a pulsation chamber outside the liner between the liner and the teat cup. The milk flow passage within the liner supplies milk to a milking claw which also receives milk from milk flow passages of other liners of other teat cups.
Simply supplying a constant vacuum to the teat is not desirable because it causes the tissue of the teat to become engorged with blood and lymph. When these fluids are confined to their normal spaces within the teat, the condition is called congestion. When the fluids leave their normal spaces, it is called oedema. These conditions may result in pain or discomfort to the mammal being milked, and swelling of the tissue which may constrict the duct through which milk is being withdrawn, thereby slowing the flow of milk. The slowing of milk flow due to the effects of congestion may be accompanied by a reduced volume of milk available for removal because the discomfort may interfere with the milk ejection reflex by which the mammal presents her milk to the teat.
Various attempts have been made to ameliorate the undesirable effects of vacuum on the teat by carefully shaping the teat cup and liner to support the teat as well as possible, and by periodically relieving the vacuum to the teat. The liner periodically collapses around and below the teat, providing massage to the teat. The massage compresses the end of the teat, thereby actively forcing fluids out of the teat apex. The massaging action of the liner also provides stimulation to the teat whereby the milk ejection reflex is strengthened. In some cases, the milk ejection reflex may be elicited solely by the action of the pulsating liner. Various types of liners are known in the art, for example "A Comparison Of The Milking Characteristics Of Teat Cup Liners" I. McD. Gibb and G. A. Mein, The Australian Journal of Dairy Technology, December, 1976, pages 148-153, and U.S. Pat. Nos. 2,997,980, 3,096,740, 4,315,480, 4,324,201, 4,530,307, 4,745,881, 4,756,275 and 4,869,205. The milking cycle has an on portion and an off portion. Milk is withdrawn from the teat through the liner to the claw during the on portion. During the off portion, the closed liner stops milk flow from the teat.
In one aspect of the present invention, a new combination is provided using positive pressure with a thin-walled floppy liner. Thin-walled floppy liners are known in the prior art, "Teat Cup and Claw" D.S.M. Phillips, Proceedings of Third Australian Machine Milking Conference, Hobart, Tasmania, 1965, pages 132-143. The use of positive pressure in the milking cycle is also known in the prior art: "Proceedings of the Symposium on Machine Milking 1968" G. Wehowski, The National Institute for Research in Dairying, Shinfield, Reading, England, 1969, pages 134-135; "Responses of the Bovine Teat to Machine Milking: Measurement of Changes in Thickness of the Teat Apex", Jorn Hamann and Graeme A. Mein, Journal of Dairy Research (1988), 55, 331-338; "Measurement of Machine-Induced Changes in Thickness of the Bovine Teat", Jorn Hamann and Graeme A. Mein, Journal of Dairy Research (1990), 57, 495-505; "Recent Developments in Milking Machine Research", Graeme A. Mein, 29th Annual Meeting National Mastitis Council, Inc., Louisville, Kentucky, Feb. 12-14, 1990, pages 3-13.
Though thin floppy liners have been known for some time, they have not been successfully used. Observed results include congestion, oedema, and slow milking. In the present invention, these failures are overcome by using positive pressure during the off portion of the milking cycle. In the present invention, the liner is a thin-walled non-distensible floppy member substantially conforming its shape to the teat, and of itself providing substantially no load on the teat. The use of such liner together with the application of positive pressure, relative to atmospheric pressure, provides a combination in which the main force applied to the teat during the off portion of the milking cycle is due to the positive pressure in the pulsation chamber which is uniformly applied at a controlled level along the barrel of the teat, and not just to the tip of the teat. A similar compressive load is applied to all the teats irrespective of their shape and size when the liner is compressed in each pulsation cycle. The cyclic compressive load is applied uniformly over most of the teat surface and controlled at a predetermined physiologically acceptable level by the pressure in the pulsation chamber.
Prior uses of cyclic application of positive pressure in the pulsation chamber have improved blood circulation, but have resulted in greater damage to the lower tip of the teat. Such prior uses involved thicker walled liners, and only the lower tip of the teat is subjected to cyclic compression by the closing liner. In the latter applications, the load varies with shape and size of the teat and with the degree of congestion of the teat. Furthermore, the high localized force results in varying degrees of hyperkeratosis around the external teat orifice. Furthermore, the barrel of the teat is not squeezed by the closure of such liner. Hence, the teat wall becomes thicker because of increased congestion and oedema, especially near the end of milking, i.e. during the low flow rate period or at the end of this period when no milk is flowing.
In the present invention, a controlled cyclic pressure is applied to the lower tip of the teat and along the barrel of the teat thereabove by means of a thin-walled floppy non-distensible liner, and blood circulation is maintained at a physiologically acceptable level within the walls of the teat barrel as well as the teat lower tip. The combination of controlled positive pressure and a thin non-distensible liner minimizes congestion, oedema, and damage to the lower tip of the teat. Teats are softer after milking, and teat condition is improved.
In another aspect of the invention, a thin-walled floppy liner is operated as a pressure switch limiting the amount of negative pressure applied to the lower tip of the teat. A negative first pressure is applied through the claw to the milk flow passage at the lower end of the liner. Pressure in the pulsation chamber is decreased during the on portion of the milking cycle to a negative second pressure. The second pressure is greater than the first pressure. The thin-walled floppy liner is closed and blocks communication of the negative first pressure to the lower tip of the teat and limits the amount of negative pressure applied to the lower tip of the teat to the noted negative second pressure acting on the thin-walled floppy liner engaging the lower tip of the teat. Milk flow from the lower tip of the teat within the thin-walled floppy liner increases the pressure within the thin-walled floppy liner to equalize and slightly exceed the pressure in the pulsation chamber outside the thin-walled floppy liner to slightly open the milk flow passage until milk flow from the lower tip of the teat decreases to reduce the pressure within the thin-walled floppy liner such that the latter closes. The pressure in the pulsation chamber is increased during the off portion of the milking cycle to a positive third pressure to collapse the thin-walled floppy liner and tightly close the milking passage and to apply the positive third pressure along the teat by acting on the thin-walled floppy liner engaging the teat.
In another aspect, the invention reduces the chances of cross-contamination between teats. As the liner opens and closes, there is a volume change within the liner below the teat which displaces and moves air back and forth. This volume change and air movement raises the possibility of cross-contamination from another teat through the claw. Thus, infection of one teat may spread to other teats. The present invention only partially opens the liner with minimum volume change below the teat to permit milk flow, which minimum volume change below the teat reduces the chances of cross-contamination from another teat. The invention enables the noted partial opening of the liner without resorting to hydraulic milking, "Hydraulic Milking-Control Within The Teat-Cup", R.J. Grindal, Proceedings of International Mastitis Symposium, MacDonald College, Quebec, Canada, Aug. 14-15, 1987, or otherwise resorting to fluctuations in the vacuum applied through the claw or special valving in the vacuum line through the claw, European Patent 0065871, Dec. 1, 1982. The present invention enables the noted partial opening of the liner while still using a conventional vacuum system wherein a substantially constant vacuum (negative pressure) is applied through the claw to the interior of the lower end of the liner throughout the milking cycle. A differential pressure is applied across the liner during the on portion of the milking cycle such that the liner only partially opens, with minimum volume change within the liner below the teat, but enough to permit milk flow.